Extended π-Conjugated System in Organic Cathode with Active C═N Bonds for Driving Aqueous Zinc-Ion Batteries

Organic compounds have recently been demonstrated to be alternative cathodes to inorganic ones for aqueous zinc-ion batteries (ZIBs), while the limited electrochemical performance greatly restricts their applications, which is partly attributable to their small π-conjugated systems. Here, to extend the π-conjugated system, diquinoxalino[2,3-a:2′,3′-c]phenazine (DQP) was designed and prepared, intriguingly exhibiting an ultrahigh capacity of 413 mA h g–1 at 50 mA g–1 for ZIBs. In addition, the combination of detailed density functional theory calculations and ex situ characterization techniques, such as IR and X-ray photoelectron spectroscopy spectra, clearly reveals the electrochemically active C═N bonds transformation in charging and discharging circulation. Moreover, the results also demonstrate that the extended π-conjugated system with active C═N bonds is associated with enhanced electrochemical stability, conductivity, and reversible capacity. Besides, owing to its excellent insolubility in water, DQP also delivers high capacity retention of 86% after 1000 cycles at 5 A g–1. Thus, this work provides a reasonable strategy for organic cathodes applied in aqueous ZIBs.